Is my postfix is hacked?

Yesterday I analyzed mail logs and noticed something really strange. I think my postfix is hacked. We do not use our mail server too much, but maillog is full of unrecognized records. Here is the part of it:

So as I understand I have relay opened. Should I simply make smtpd_sasl_auth_enable = yes to NO ? And what I will loose after that? I do not so good in all this... I hope you will help me to understand.

I do not think that it is from guestbooks/forms. What I have done: I stopped postfix for about 3 hours. Then I started it again and look into logs. Immediately after start I got tons of mails in queue (I am not posting all of them):

the reason i believe you need this is for avoiding spammers
to querie your mail server for valid users (they also use VRFY and EXPN commands as well).

the use of luser_relay is for creating a bucket ,so that your system
will never try to send back mail telling that the x mailbox doesnt exists,
the drawback of this approach is that if a valid user sends mail to one
of yours account but he mistyped his mail,he will never know that his
mail never reached the intended recipient, the advantage is that
your queue will never be full with postfix trying to send back notifications
to spammers (who will probably provided erroneous from: address..)

I've made the changes mentioned maikcat, also erased the deferred queue, with postsuper -d ALL deferred command.
Apparently now the queue is empty, but I have to continue to monitor the operation of the server.

Sry for the delay... Yes I have A, MX, and txt SPF record for the domain.
The only thing I can get to be in the unusual configuration is that I have 2 MX records plus, that not responding "the concept of nolisting"